[igraph] bipartite from edgelist?

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i have some order records including buyer ids and seller ids, we can consider it as an edgelist, in which the buyers and sellers are the nodes.

i want to consider it as an bipartite network including buyers and sellers, but how can i bipartite it into buyers network and sellers network, please?

if i call bipartitie.mapping, it returns False...

Thanks

Gang